As Donald Trump’s legal challenges multiply, so do comparisons of him to Richard Nixon, the only president ever removed from office. We’re getting used to headlines like “How Trump’s scandals mimic Watergate,” “Trump is going full Nixon on Mueller” and “Who’s worse, Trump or Nixon?”

Turn on MSNBC on a given night, and you’ll hear veterans of the Watergate scandal like John Dean and the prosecutor Jill Wine-Banks explaining the parallels -- the special prosecutor, the witnesses who may “flip,” the possible subpoena of the president.

At the same time, however, prominent liberals, including Democratic Rep. Adam Schiff of California and Harvard law professor Laurence Tribe, are trying to tamp down talk of impeachment.

Why the caution? One practical explanation is the headcounting. Democrats had large majorities in both the House and the Senate in July 1974, when the House Judiciary Committee voted in favor of three articles of impeachment. In his resignation speech Nixon said he was quitting because he no longer had a “strong enough political base in the Congress.”

In the current debate, we’ve become used to these reminders that Watergate was a political story, not just a legal one. But the lessons are more numerous -- and more deeply rooted -- than we may think. While many Americans may be hoping for a Watergate-style salvation from Trump, think again: It helped Democrats for a total of four years but also set the stage for a powerful conservative backlash. America in 2018 looks a lot like America in the 1970s -- divided, polarized, riven with tribal antagonisms.

Nixon was elected -- and re-elected -- in a time of bitter disagreements over wrenching issues like the Vietnam War and civil rights. His approach was to pit one group against another. This “positive polarization” exploited what his speechwriter William Safire called the “us-against-them syndrome.”

Once in office, Nixon did not let up. In fact, some of his more provocative actions seem like rehearsals for Trump’s. After the “hard hat riot,” in which New York construction workers, some holding signs that said “America, Love It or Leave It,” physically assaulted anti-war demonstrators, Nixon invited the head of the construction workers union to the White House -- and later made him secretary of labor.

And like Trump’s, Nixon’s White House was a hotbed of conspiratorial thinking. One of his most brilliant advisers, the Democrat Daniel Patrick Moynihan, publicly claimed that reporters at the New York Times and the Washington Post were “hostile to American society and American government.”

At the time, Moynihan’s musings seemed overheated, like today’s talk of the “deep state” -- until Daniel Ellsberg, a policy analyst who had worked on Nixon’s transition team, began giving classified documents, the Pentagon Papers, to reporters at the Times and the Post. In retaliation the White House created its team of “plumbers” to plug leaks, thus beginning the chain of events that led to Watergate.

Nixon’s aide Patrick Buchanan described the enemy’s strategy. “What the left has in mind is, not just running to ground their adversary of a quarter century,” Buchanan wrote, “but rendering ‘inoperative’ the political verdict” of his landslide re-election.

Another conservative who saw it this way -- he later became Buchanan’s boss -- was Ronald Reagan. The governor of California when the Watergate break-in happened, he privately called the investigation a “lynching” and publicly praised Nixon when he refused at first to let his aides testify to the Senate. “This man has just been elected,” Reagan explained. And the party had a “two-to-one majority philosophically.”

As for the burglars caught in the Democratic National Committee headquarters, Reagan said they were “well-meaning individuals,” not “criminals at heart.” This became “a laugh line,” Perlstein reports. Journalists, in particular, found it absurd that Reagan, the apostle of “law and order,” was coming to the defense of felons.

Reagan didn’t care. He “stuck with Nixon during the Watergate scandal long after his advisers had concluded that the president was a liar and a lost cause,” writes Reagan’s biographer Lou Cannon.

It looked foolhardy. But in fact there were two Watergates. One had come to an end when Nixon’s successor, Gerald Ford, assured the country, “Our long national nightmare is over. Our constitution works; our great Republic is a government of laws and not of men. Here the people rule.”

The second Watergate lived on for conservatives who believed it was really about what the revisionist Nixon scholar Joan Hoff has called “the insatiable desire to ‘get’ Richard Nixon on the part of a tiny group of New York and Washington reporters.”

Post-Watergate politics was, in effect, a referendum on these two competing versions. Liberals emphasized the rule of order, and the dangers of an increasingly imperial and corrupt presidency. Conservatives argued that the country was under siege from the people who had brought Nixon down, a “new class” or “elite” who disdained the values and ideals of middle America.

Initially, liberals had the advantage. Nixon resigned in disgrace, and a new generation of reform Democrats were swept into office, first in the post-Watergate midterm elections and then in 1976, when the squeaky-clean Democrat Jimmy Carter was elected.

But those victories were short-lived. Many of the “Watergate babies” in Congress came from affluent suburbs, where good-government issues, like campaign-finance reform, resonated. But they didn’t speak to a lot of voters, including blue-collar Democrats, who had voted for Nixon and then been slow to accept his guilt in Watergate. Carter too failed to connect with those voters.

Four years later, the Republicans roared back, led by Nixon’s staunch defender, Ronald Reagan.

In heartland districts like Michigan’s Macomb County outside Detroit, “Reagan Democrats” rejected their old party. It happened again in 2016, when Macomb voters who had helped elect Barack Obama in 2008 and 2012 switched over to Trump.

None of this is lost on Trump, who returned to Macomb for a rally on the same night that beltway journalists gathered in tuxes and evening gowns for the White House Correspondents’ Dinner.

This is the Watergate legacy that Democrats fear, and they have every reason to do so.

Sam TanenhausSam Tanenhaus, the author of “The Death of Conservatism” and “Whittaker Chambers,” is working on a biography of William F. Buckley Jr. -- Ed.